In the engine compartment of modern vehicles, in both passenger and utility fields, sound-absorbing parts in the form of absorbers are increasingly employed for reducing engine noise. These absorbers, which are predominantly designed as formed parts, have an influence on the exterior and interior noise of the vehicles. The formed parts predominantly employed today which are made of non-woven fabrics (e.g., of cotton) or of PU foam typically have deflection temperatures under load of up to about 160° C. For higher thermal loads, these formed parts are partially or completely backed with aluminum foils as heat reflectors on the surface facing the heat source in order to protect the non-woven fabrics lying behind.
From DE 36 01 204 A, an absorptive formed part consisting of several layers of non-woven is known which may serve for noise-damping linings for the engine compartment of motor vehicles. The absorptive formed part consists of a cover layer of plastic fibers on the engine side, a contiguous heat-insulating and sound-absorbing layer of inorganic fibrous material having a high deflection temperature, and another absorbing layer of organic fibers.
DE 38 18 301 C also describes a noise-damping formed part for the engine compartment of motor vehicles in which an inorganic fibrous material bonded by a binder and having a high deflection temperature is covered, on the engine side, with a carbon fibrous material through a bonding agent containing a melamine resin. This formed part is said to have a good sound absorption and to be also suitable as a thermal insulation in a temperature range of up to about 500° C.
DE 42 11 409 A1 relates to a self-supporting, heat-insulating and sound-absorbing lining for combustion engines of motor vehicles which consists of several layers compression-molded under the action of pressure and heat to form zones having a predefined compression. On the engine side, the lining consists of a thicker heat-insulating and sound-absorbing layer of an inorganic fibrous material which is covered by a carbon fibrous material. A thicker layer of inorganic fibrous material facing away from the engine will cure into a self-supporting support layer. On the body side, this support layer may be covered with a layer of a polyester non-woven or polyacrylonitrile fibers.
A heat-insulating and sound-absorbing lining which is also often employed in the automobile field is based on melamine resin foams to which temperature-resistant cover layers are applied on one or both sides. According to DIN 4102, melamine resin foams are considered flame-resistant, and due to their behavior in fire, are to be classified into class B1. Due to its long-term thermal stability of −40° C. to 150° C. and its long-term temperature resistance of 200° C. for three weeks, this material is particularly suitable for preparing linings for the engine compartment of motor vehicles. However, this material is extraordinarily expensive so that it has been the object of the present invention to provide linings for the engine compartment of motor vehicles which are comparable therewith regarding the heat insulation and sound absorption, but involving a significant reduction in costs as compared to the prior art.
DE 198 21 532 A1 describes heat-insulating and sound-absorbing linings (sound absorbers) for the engine compartment of motor vehicles, consisting of a cover layer on the engine side, and in contact therewith an acoustically insulating thermoset foam layer having a long-term thermal stability of up to 180° C. and a long-term temperature resistance of 200° C. for three weeks, of a thickness of less than 5 mm, and in contact therewith an acoustically insulating layer of plastic foam, particle composite foam or non-woven fabric, consisting of native or synthetic fibers and mixtures thereof, needled or not, and in contact therewith a cover layer facing away from the engine side. Thus, the lining parts are particularly suitable for the lining of build-in components, body parts or the like of automobiles, heat-emitting machines and aggregates, especially of sound-absorbing elements for protection against too high thermal loads from machine guidance systems, catalyst parts or the like, especially in the engine compartment of motor vehicles.
In this case, the geometry of the lining part depends on the interior side of the front access door and the space conditions in the engine compartment. The lining parts are attached, for example, by engaging them into a hole pattern in the interior zone of the front access door. They are held by as few spreading rivets as possible. In the region of the bulkheads within the engine compartment, it is possible to apply lining parts between the body and the engine, the lining parts preferably being attached to the body using coarse thread bolts or snap fasteners (or sheet metal nuts). The lining parts serve for sound absorption of the engine noise.
In the region of the wheel housing in the engine compartment, the lining parts on the engine side are positioned in the air collection space. They prevent engine noise from intruding into the interior space and are preferably also attached with coarse thread bolts or snap fasteners. In the region of the bulkhead of the engine compartment, the lining parts serve, for example, for covering the body-in-white from the cross member bulkhead or disk gap to the level of the tunnel for completing the underside paneling. Optionally, the lining parts may contain openings for ducts of the air conditioning system. In the region of the tunnel exterior, the lining parts may also be inserted between the transmission or the exhaust gas train and the floor pan. In this case too, it is particularly preferred to attach them with coarse thread bolts and/or snap fasteners, for example, sheet metal nuts.
When the lining parts are employed in the region above the clean-air panel, it is covered from above and is then attached there. It is then positioned above the left and right bulkheads of the engine compartment.
There is no drop of strength below the initial value by the action of heat when used as directed.
DE 41 14 140 A1 relates to sheet fabrics in which the bonding of the fibers is effected through thermoplastic polyamides. The advantage of the sheet fabrics is their suitability for recycling after use. In addition, in the preparation of the sheet fabrics, disadvantages put up with to date, offensive smells and undesirable decomposition products are excluded.
DE 43 05 428 C1 describes a floor covering formed from a non-woven sheet which has, on the bottom side, naps in island and integrally designed fashions which consist of a plurality of individual fibers. On its top side, the floor covering preferably has a structure. The structures of both sides are formed by needling. When the floor covering is laid, the naps are supported by the substrate floor. This creates a channel system on the bottom side of the floor covering which favors the draining of water. A thus designed floor covering is preferably employed in the outdoor field, for example, as a tennis court covering, wherein granules can be introduced into the recesses on the top side.
DE 44 44 030 describes a floor covering, especially for tennis courts. It consists of a carpet-type base covering and an anti-slip scattering applied thereto which consists of individual loose particles. The particles of the anti-slip scattering are respectively extruded from plastic with a substantially defined cross-sectional shape and length, the respective length being at least approximately equal to the particle width or height running about midway through the cross-section.
DE 198 12 925 A1 describes three-dimensional, dimensionally stable formed parts based on structured needle-punched webs. The needle-punched webs of thermoplastic fibers having a first layer of a mixture of polypropylene (PP) fibers and polyethylene (PE) fibers and a second and optionally further layers of a mixture of PP fibers and PE fibers is prepared from bicomponent fibers consisting of a mixture of PP and PE or from a mixture of such bicomponent fibers with PP fibers and/or PE fibers, wherein the two layers are bonded within and between them both by needle punching and by molten or surface-molten fibers or fiber parts of the PE fraction of the two layers.
DE 44 28 613 A1 describes a sound-absorbing and heat-insulating material. It describes, in particular, to combine the characteristics of highly condensed materials with those of flexible sound-absorbing bulky materials with good flow characteristics by the combination of several materials and layer thicknesses with a distance-fixed structure, in order to manage both tasks as much as possible. This was achieved by the use of predominantly recycled fibrous materials which, due to their wide variety of geometries, irregularly form artificial reflecting and absorbing barriers within the layers, and with fillers in the fiber layers, as well as by a multilayer structure making use of all technical possibilities of non-woven and fiber-laying technology, as well as in combination with non-textile materials.
DE 44 22 585 C1 describes an air-noise absorbing formed part and a method for its preparation. In particular, it describes an air-noise absorbing formed part consisting of first and second semifinished products each consisting of at least one layer of non-woven material, wherein said semifinished products are arranged adjacent to each other at a distance in the direction of the incoming air noise to form at least one hollow space, wherein said semifinished products are functionally arranged in series and supported on each other, and wherein the second semifinished product, which faces away from the air noise, has a higher acoustic impedance as compared to the first semifinished product, which faces towards the air noise. The acoustic impedance of the second semifinished product is 1.25 to 5 times as high as the acoustic impedance of the first semifinished product, and the first semifinished product has an acoustic impedance of 40 to 80 Rayl, and the second semifinished product has an acoustic impedance of 90 to 150 Rayl.
A common feature of the above mentioned prior art is a relatively narrow sound-absorption frequency spectrum when the sound absorber consists of several interconnected non-woven sheets. Alternatively, sound absorbers are known which have a heavy layer and thus act according to the spring/mass principle. However, such sound absorbers are relatively heavy, and the heavy layer, which is mostly made of ethylene/vinyl acetate copolymers having a high content of fillers, is little suitable for recycling. Although the sound absorption is satisfactory within a range of from 100 to 500 Hz, it is absolutely unsatisfactory in a higher frequency range.
In contrast, the object of the present invention is to improve sound absorption especially in the particularly interesting frequency range of from 200 to 800 Hz.